hgweb: add a sendtemplate() helper function This pattern is common. Let's make a helper function to reduce boilerplate. We store the "global" template on the requestcontext instance and use it. The templater used by the helper function is the same templater that's passed in as an argument to the @webcommand functions. It needs to be this way because various commands are accessing and mutating the defaults on the templater instance. Differential Revision: https://phab.mercurial-scm.org/D2799